Abstract:

A zirconium-loaded fibrous adsorbent material having phosphoryl groups
which is produced by first grafting a reactive monomer having phosphoryl
groups onto a polymeric substrate and then loading zirconium. One or more
methods of using the zirconium-loaded fibrous adsorbent material to
recover arsenic, phosphoric ions, and/or fluoride ions are disclosed.

Claims:

1. A method of recovering arsenic using a zirconium-loaded fibrous
adsorbent material having phosphoryl groups, which comprises subjecting
said adsorbent material to passage of an arsenic containing liquor at a
space velocity of 64-1300 [1/h] under acidic conditions at a pH of less
than 7.

2. A method of recovering phosphoric ion using a zirconium-loaded fibrous
adsorbent material having phosphoryl groups, which comprises subjecting
said adsorbent material to passage of a phosphoric ion containing liquor
at a space velocity of 64-1300 [1/h] under acidic conditions at a pH of
about 1.5.

3. A method of recovering fluoride ion using a zirconium-loaded fibrous
adsorbent material having phosphoryl groups, which comprises subjecting
said adsorbent material to passage of a fluoride ion containing liquor at
a space velocity of 64-1300 [1/h] under acidic conditions at a pH of less
than 7.

4. The method of claim 1, wherein the zirconium-loaded fibrous adsorbent
material has a zirconium content in an amount of 4.0 or 4.2 mmol/g.

5. The method of claim 4, wherein the fibrous material is selected from
the group consisting of a fiber, a filament, a nonwoven fabric and a
woven fabric.

6. The method of claim 5, wherein the fiber is selected from the group
consisting of polypropylene, polyethylene and polyester.

7. The method of claim 5, wherein the fiber is selected from the group
consisting of polypropylene and polyethylene.

8. The method of claim 1, wherein the phosphoryl group is selected from
the group consisting of mono(2-methacryloyloxyethyl)acid phosphate,
di(2-methacryloyloxyethyl)acid phosphate, mono(2-acryloyloxyethyl)acid
phosphate, di(2-acryloyloxyethyl)acid phosphate, and mixtures thereof.

9. The method of claim 1, wherein the phosphoryl groups of the
zirconium-loaded fibrous adsorbent material are phosphoryl groups of a
reactive monomer comprising a material of
formula:CH.sub.2.dbd.C(CH3)COO(CH2)lOCO--R--CO--OPO(OH)R'w-
herein R is an optionally substituted (CH2)m group or
C6H4 group, wherein R' is a hydroxyl group or a
CH2=C(CH3)COO(CH2)nOCO--R--CO--O-group, wherein l, m
and n are each independently an integer of 1-6.

10. The method of claim 1, wherein the wherein the fibrous material is a
filter.

11. The method of claim 2, wherein the zirconium-loaded fibrous adsorbent
material has a zirconium content in an amount of 4.0 or 4.2 mmol/g.

12. The method of claim 2, wherein the fibrous material is selected from
the group consisting of a fiber, a filament, a nonwoven fabric and a
woven fabric.

13. The method of claim 12, wherein the fiber is selected from the group
consisting of polypropylene, polyethylene and polyester.

14. The method of claim 2, wherein the phosphoryl group is selected from
the group consisting of mono(2-methacryloyloxyethyl)acid phosphate,
di(2-methacryloyloxyethyl)acid phosphate, mono(2-acryloyloxyethyl)acid
phosphate, di(2-acryloyloxyethyl)acid phosphate, and mixtures thereof.

15. The method of claim 2, wherein the phosphoryl groups of the
zirconium-loaded fibrous adsorbent material are phosphoryl groups of a
reactive monomer comprising a material of
formula:CH.sub.2.dbd.C(CH3)COO(CH2)lOCO--R--CO--OPO(OH)R'w-
herein R is an optionally substituted (CH2)m group or
C6H4 group, wherein R' is a hydroxyl group or a CH.sub.2.dbd.C
(CH3)COO(CH2)nOCO--R--CO--O-group, wherein l, m and n are
each independently an integer of 1-6.

16. The method of claim 2, wherein the wherein the fibrous material is a
filter.

17. A method of forming a zirconium-loaded fibrous adsorbent material
having phosphoryl groups, the method comprising:(a) grafting a reactive
monomer having phosphoryl groups onto a polymeric substrate; and(b)
loading zirconium such that the zirconium-loaded fibrous adsorbent
material has a zirconium content in an amount of 4.0 or 4.2 mmol/g.

18. The method of claim 17, wherein:(i) the polymeric substrate is
selected from the group consisting of a fiber, a filament, a nonwoven
fabric and a woven fabric,(ii) the reactive monomer comprises a material
of formula:CH.sub.2.dbd.C(CH3)COO(CH2)lOCO--R--CO--OPO(OH)-
R'wherein R is an optionally substituted (CH2)m group or
C6H4 group, wherein R' is a hydroxyl group or a
CH.sub.2.dbd.C(CH3)COO(CH2)nOCO--R--CO--O-group, wherein
l, m and n are each independently an integer of 1-6, and(iii) the
phosphoryl group is selected from the group consisting of
mono(2-methacryloyloxyethyl)acid phosphate,
di(2-methacryloyloxyethyl)acid phosphate, mono(2-acryloyloxyethyl)acid
phosphate, di(2-acryloyloxyethyl)acid phosphate, and mixtures thereof.

19. The method of claim 18, wherein the fiber is selected from the group
consisting of polypropylene, polyethylene and polyester.

20. The method of claim 19, wherein the grafting comprises graft
polymerization further comprising:(a1) generating reaction active points
in the polymeric substrate by(a2) exposing the polymeric substrate to
electron beam radiation or γ-ray radiation in a nitrogen
atmosphere,(a3) exposing the polymeric substrate to plasma in a nitrogen
atmosphere, or(a4) exposing the polymeric substrate to radical initiators
selected from the group consisting of azobisisobutyronitrile and benzoyl
peroxide; and(a5) contacting the reaction active points with the reactive
monomer.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001]This application is a divisional application of U.S. Ser. No.
10/732,232 filed in the U.S. Patent and Trademark Office on Dec. 11,
2003, which claims the priority benefit of Japanese Patent Application
No. 2002-358915 filed on Dec. 11, 2002 in Japan. The entire contents of
each of these applications (U.S. Ser. No. 10/732,232 and Japanese Patent
Application No. 2002-358915) are incorporated herein by reference in
their entirety.

BACKGROUND

[0002]This invention relates to an adsorbent material for recovering and
removing objectionable substances, in particular, arsenic that are
contained in environmental water and liquid wastes such as waste water
from plants. One or more embodiments of the invention also relate to a
method of synthesizing the adsorbent material.

[0003]Research and development efforts have recently been made on
materials capable of trapping metals contained in environmental water
bodies such as rivers and the sea and this has led to the discovery that
cation exchange resins using phosphoric acid as exchange groups can
adsorb metal ions present in rivers, lakes and wastewater from plants
(see, for example, Akinori Joh et al., "Cation exchange resins using
phosphoric acid as exchange groups--Their selectivity for metal ions and
applications" in PHOSPHORUS LETTER, Japanese Association of Inorganic
Phosphorus Chemistry, Feb. 1, 2001, vol. 40, pp. 16-21).

[0004]Further, the present inventors developed a metal adsorbent material
that had a monomer with phosphoryl groups grafted onto a polymeric
substrate (see, for example, Japanese Patent Application No.
2002-262502).

[0005]In the art of recovering and removing objectionable substances in
the environment, particularly arsenic, two major methods have so far been
practiced, one relying upon coagulating sedimentation and the other using
chelating resins (see, for example, Xiaoping Zhu et al., "Removal of
arsenic(V) by zirconium(IV)-loaded phosphoric acid chelating resin" in
"SEPARATION SCIENCE AND TECHNOLOGY", America, Marcel Dekker, Inc., 2001,
36(14), pp. 3175-3189).

[0006]However, the conventional adsorbent materials can adsorb arsenic
only slowly. If arsenic is recovered and removed by coagulating
sedimentation or with the aid of adsorbent materials in bead form,
considerable inconvenience in handling has been met during the process of
removal or in subsequent operations.

[0007]In addition, the conventional arsenic adsorbent materials are mostly
synthesized by common radical polymerization and their structure for
adsorption of arsenic is so unstable that it is prone to leak out even if
it is adsorbed.

[0008]According to the Basic Environment Law which provides for the water
quality guidelines for public waters, arsenic should not be discharged at
concentrations higher than 0.1 ppm and its content in the environment
should not exceed 0.01 ppm. Thus, the removal of arsenic is absolutely
necessary.

SUMMARY OF EMBODIMENTS OF THE INVENTION

[0009]An object, therefore, of one or more embodiments of the present
invention is to provide an adsorbent material that allows for faster
adsorption of arsenic and anion such as phosphoric ion and which can
remove them even if they are present at extremely low concentrations.

[0010]Another object of one or more embodiments of the invention is to
provide an adsorbent material that is easy to handle during or after
adsorptive removal of arsenic and which is capable of efficient
adsorption of arsenic.

[0011]In order to attain those objects, the present inventors made
intensive studies and completed the present invention which relates to a
zirconium-loaded fibrous adsorbent material having phosphoryl groups.

[0012]The zirconium-loaded fibrous adsorbent material of one or more
embodiments of the invention having phosphoryl groups is produced by
first grafting a reactive monomer having phosphoryl groups onto a
polymeric substrate and then loading zirconium.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]The drawing figures are non-limiting and illustrative of one or more
embodiments of the claimed invention.

[0014]FIG. 1 is a graph showing the pH dependency of the performance of
the zirconium-loaded adsorbent material of an embodiment of the invention
in adsorbing arsenic;

[0015]FIG. 2 is a graph showing the dependency on flow rate of arsenic
adsorption by the zirconium-loaded adsorbent material an embodiment of
the invention; and

[0016]FIG. 3 is a graph showing the dependency on arsenic's concentration
of the zirconium-loaded adsorbent material of an embodiment of the
invention.

[0017]FIG. 4 is a graph showing the phosphoric ion adsorption
characteristics of the adsorbent material of an embodiment of the
invention.

[0018]FIG. 5 is a breakthrough curve of phosphoric ion on the adsorbent
material of an embodiment of the invention.

[0019]FIG. 6 is a breakthrough curve of fluoride ion on the adsorbent
material of an embodiment of the invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0020]The adsorbent material of one or more embodiments of the invention
is a zirconium-loaded fibrous adsorbent material having phosphoryl groups
and it is produced by first grafting a reactive monomer having phosphoryl
groups onto a polymeric substrate and then loading zirconium.

[0021]In one or more embodiments of the invention, fibers of
polypropylene, polyethylene, polyester or composites thereof can be used
as the polymeric substrate and they may take on various forms including
short fiber, filament, nonwoven fabric or woven fabric.

[0022]The first step in the synthesis of the adsorbent material of one or
more embodiments of the invention is preparing an adsorbent precursor
(hereunder sometimes referred to as the "graft product") by grafting a
reactive monomer having phosphoryl groups onto the polymeric substrate.

1. Preparing the Adsorbent Precursor (Graft Product)

[0023]The method for preparing the graft product may comply with the
conditions for synthesis disclosed in Japanese Patent Application No.
2002-262502. Specific procedures and conditions of the method are
described below.

[0024]A monomer having mono- or difunctional phosphoryl groups may be
introduced into the polymeric substrate and specific examples include:

mono(2-methacryloyloxyethyl)acid phosphate

CH2═C(CH3)COO(CH2)2OPO(OH)2;

di(2-methacryloyloxyethyl)acid phosphate

[CH2═C(CH3)COO(CH2)2O]2PO(OH);

mono(2-acryloyloxyethyl)acid phosphate

CH2═CHCOO(CH2)2OPO(OH)2;

di(2-acryloyloxyethyl)acid phosphate

[CH2═CHCOO(CH2)2O]2PO(OH); and

mixed monomers thereof.

[0025]In the case of using mixed monomers, the mixing ratios of the
respective monomers may be changed appropriately.

[0026]A type of monomer having the following structure may also be used as
the reactive monomer:

CH2═C(CH3)COO(CH2)lOCO--R--CO--OPO(OH)R'

, wherein R is an optionally substituted (CH2)m or
C6H4; R' is a hydroxyl group or
CH2═C(CH3)COO(CH2)nOCO--R--CO--O-- group; l, m
and n are each independently an integer of 1-6.

[0027]Graft polymerization can be effected by first generating reaction
active points in the polymeric substrate and then bringing it into
contact with the reactive monomer.

[0028]Reaction active points can be generated by either one of the
following methods (a)-(c).

(a) Exposure to Radiation

[0029]The polymeric substrate as preliminarily nitrogen purged is exposed
to radiation in a nitrogen atmosphere either at room temperature or under
cooling with Dry Ice. The radiation to be employed is electron beams or
γ-rays. The exposure dose may be determined appropriately on the
condition that it be sufficient to generate reaction active points and it
is typically in the range of 50-200 kGy.

(b) Exposure to Plasma

[0030]The polymeric substrate as preliminarily nitrogen purged is exposed
to plasma in a nitrogen atmosphere at room temperature. The exposure
continues for 1-24 hours using rf waves at 10 MHz or higher.

[0032]While graft polymerization can be effected in a nitrogen atmosphere,
the concentration of oxygen in the atmosphere is preferably low in order
to achieve higher values of percent grafting. The term "percent grafting"
as used herein means the ratio in weight percentage of the reactive
monomer to the polymeric substrate onto which it has been grafted. The
reaction temperature which depends on the reactivity of the reactive
monomer is generally between 40 and 60° C. The concentration of
the monomer suffices to range from 10 to 30% of the solvent. The reaction
time which is generally 1-48 hours can be determined depending upon the
reaction temperature and the percent grafting required.

2. Synthesis of the Zirconium-Loaded Adsorbent Material

[0033]The adsorbent material of one or more embodiments of the invention
can be produced by loading the thus prepared graft product with
zirconium.

[0034]The graft product is subjected to passage of a zirconium compound in
solution at a pH of 0.5-2 for 1-24 hours at a flow rate of 100 mL/h. The
zirconium compound that can be used in one or more embodiments of the
invention is a zirconium(IV) compound, a zirconium(III) compound or a
zirconium(II) compound and may be exemplified by zirconic acid, zirconate
(a conventoinal oxo-acid salt of zirconium(IV)), zirconate (which is not
an oxo-acid of zirconium), etc. Specific examples of zirconium compounds
in solution include solutions of zirconium nitrate, zirconium sulfate,
zirconium chloride and zirconium oxide, as well as an analytical standard
solution of zirconium. The concentration of zirconium compounds in
solution can be adjusted appropriately.

[0035]In order to subject the graft product to passage of zirconium
compounds in solution, any means known to the skilled artisan may be
employed, such as stirring the solution in which the graft product is
immersed or passing the solution through a column packed with the graft
product. Preferably, the desired product can be obtained by stirring 10
mmol/L of zirconium nitrate in solution at a pH of 1 for one hour as it
contains the graft product immersed therein or by passing the solution
through a column packed with the graft product.

[0036]The arsenic adsorption characteristics of the adsorbent material of
one or more embodiments of the invention are depicted in FIGS. 1-3.

[0037]FIG. 1 is a graph showing the pH dependency of arsenic adsorption at
varying pHs of an arsenic containing liquor. As one can see from FIG. 1,
the adsorbent material of one or more embodiments of the invention can
adsorb arsenic at pHs of 1-9 and its adsorbing capability is by no means
dependent on pH. It can also be seen that the difference in absorbing
capability is particularly small in the acidic range below pH=7. At each
of the tested pH values, the absorbing capability of the adsorbent
material saturated and substantially leveled off when the amount of the
effluent was about 130 times the volume of the sample.

[0038]FIG. 2 is a graph showing the dependency on flow rate of arsenic
adsorption at varying flow rates of an arsenic containing liquor. As one
can see from FIG. 2, the adsorbing capability was maintained when the
arsenic containing liquor was passed at space velocities of 64-1300 1/h
and this indicates that arsenic could be adsorbed without leakage even at
high treatment speeds. The data in FIG. 2 shows the feasibility of the
adsorbent material of one or more embodiments of the invention in
large-scale, high-speed treatments as in plants.

[0039]FIG. 3 is a graph showing the concentration dependency of arsenic
adsorption at varying concentrations of arsenic in an arsenic containing
liquor. As one can see from FIG. 3, the adsorbing capability of the
adsorbent material of an embodiment of the invention does not vary much
at arsenic concentrations of 1-5 mmol/L and can be maintained independent
of the concentration of the treating liquor.

[0040]Thus, FIGS. 1-3 show that the adsorbent material of one or more
embodiments of the invention exhibits high adsorbing capability
independent of the concentration of the treating liquor, the pH and the
treating speed.

[0041]The following examples are provided for further illustrating one or
more embodiments of the present invention but are in no way to be taken
as limiting.

Example 1

[0042]A nonwoven fabric as a polymeric substrate was subjected to graft
polymerization and the resulting graft product in nonwoven fabric form
was rendered wet by passing pure water. In the process of preparing the
graft product, the conversion (the degree of grafting) was 100-400% and
phosphoryl groups were introduced in amounts of 4-8 mmol/g. Subsequently,
the graft product was packed into an adsorption column, through which an
aqueous solution of zirconium nitrate (10 mmol/L, pH=2) was passed for
one hour at a flow rate of 100 mL/h so as to load the graft product with
zirconium. Thereafter, the column was washed with pure water until the pH
of the effluent was between 5 and 7, thereby yielding a zirconium-loaded
adsorbent material. The zirconium loading was 4.2 mmol/g. The adsorbent
material produced in Example 1 using the nonwoven fabric is not only
usable as a filter on its own; the scope of its applications can be
widened by processing it into various shapes or making a laminate of it.

Example 2

[0043]Polyethylene short fiber was used as a polymeric substrate, onto
which a reactive monomer having phosphoryl groups was grafted to prepare
a graft product. The degree of grafting was 100-300% and phosphoryl
groups were introduced in amounts of 1-8 mmol/g. An aqueous solution of
zirconium preliminarily adjusted to 10 mmol/L was treated with nitric
acid to have a pH of 1. The fibrous graft product was immersed in that
acidic aqueous solution of zirconium, which was then stirred for 1-24
hours at 25° C. The zirconium-loaded adsorbent material was
obtained and it was found to have zirconium introduced in an amount of
4.0 mmol/g.

[0044]The adsorbent material produced in Example 2 using the short fiber
has good processability and can be packed into various types of modules
including columns, thus expanding the scope of its applications.

[0045]The adsorbent material of one or more embodiments of the present
invention is synthesized by utilizing graft polymerization, so a
crosslinked structure can be easily formed within the adsorbent material.
Since this facilitates immobilization of zirconium which is responsible
for adsorbing arsenic, not only the arsenic contained in the environment
such as natural water but also other objectionable substances including
antimony and negatively charged ions such as fluoride and chloride ions
can be easily removed, thus adding potential uses including prevention of
environmental pollution and purification of potable water.

[0046]Unlike the conventional adsorbent materials that must be processed
into modules for practical use, the adsorbent material of one or more
embodiments of the invention can be directly used as a filter and permits
easy handling.

Example 3

[0047]The phosphoric ion adsorption characteristics of the adsorbent
material of one or more embodiments of the invention are depicted in FIG.
4. It was depicted by subjecting the material to a passage of phosphoric
ion containing liquors at a pH of 1.5 having various phosphoric ion
concentrations at varying contact time. Compared with the prior method of
adsorbing phosphoric ions by using a zirconium-loaded activated carbon,
the rate of adsorption obtained by the adsorbent material of one or more
embodiments of the invention is so high that the percentage of adsorption
attained up to about 100% in 2 hours.

[0048]The breakthrough curve of phosphoric ion on the adsorbent material
of one or more embodiments of the invention was depicted in FIG. 5. As
shown in FIG. 5, when the adsorbent material of one or more embodiments
of the invention was packed into a column, through which a phosphoric ion
containing liquor was passed, no phosphoric ion was leaked independent of
the phosphoric ion concentration in the liquor.

Example 4

[0049]Adsorption experiment was conducted on the adsorbent material of one
or more embodiments of the invention by using a fluoride ion containing
liquor. The liquor was prepared by adjusting pH of a standard solution of
fluorine (10 mmol) to 7. The breakthrough curve of fluoride ion on the
adsorbent material was depicted in FIG. 6. The adsorbent material of one
or more embodiments of the invention was packed into a column, through
which the liquor was passed at flow rate of 1300 h-1, 240 h-1,
and 64 h-1, in result, the breakthrough point was about 50
independent of the flow rate of the liquor.